Preventive conservation is a specialization within the conservation profession, and it addresses concerns which apply to all disciplines within the field. The goal of preventive conservation is to identify and reduce potential hazards to cultural artifacts with thoughtful control of their surroundings.
Contents |
Cultural artifacts face threats from a variety of sources on a daily basis, from thieves, vandals, and pests; to pollution, humidity, and temperature; to natural emergencies and physical forces; to all kinds of light.[1] Effects stemming from these issues can be treated and sometimes reversed with interventive conservation after the damage has occurred. However, many of the sources of danger mentioned above are controllable, and others are at least predictable. Preventive conservation strives to mitigate the occurrence of damage and deterioration through research and the implementation of procedures which enhance the safety of cultural objects and collections. The areas of particular concern with regard to the sources of damage include: environmental conditions, object handling, pest management, emergency preparedness, and duplication.[2]
Environmental conditions are highly controllable in most indoor situations. They include the temperature, relative humidity, and light levels present in a collection space on any given day. Some flexibility is naturally built in to most objects when it comes to the temperature and humidity changes they can bear, allowing for conditions to vary somewhat in response to the outdoor environment of a location.
Two types of light offer potential decay to cultural artifacts: ultraviolet (UV) and the visual light perceived by the human eye. Although they can be affected simultaneously by removing light sources, reducing overall intensity, or increasing the distance between a light source and an object, best preventive practice treats these types of light separately due to their differences.
Any storage or display situation must take into consideration the temperature at which object permanence can be optimized, and systems should be in place that aim to meet that standard, ideally in conjunction with efficient use of energy and funds. Different materials react to temperature in different ways. For example, ceramics are vulnerable to direct heat on a mechanical level, but many organic materials are at greater risk of undergoing phase transition if the temperature becomes excessively cold.[3] One rule of thumb applies across the board: the rate of chemical reactions is dependent upon temperature in such a way that higher temperatures reduce the activation energy and hasten chemical degradation processes.[4]
Human comfort levels must also be considered. Storage areas can often get away with slightly lower temperatures than display areas since they are not accessed as often, and it is most likely that those who do enter the space will be prepared for the conditions. In galleries, however, viewers must feel comfortable enough with the temperature to spend time there, otherwise the objects will simply not be viewed and lose their purpose in being on display.[3]
In recent decades it has become understood that even delicate organic materials have some elasticity in their response to relative humidity (RH) fluctuations, allowing the materials to swell or contract as necessary. This phenomenon is naturally reversible within a range of 50% ± 15% RH.[3] Destructive chemical and mechanical processes, such as hydrolysis at high RH and embrittlement and cross-linking at low RH, can be held to a minimum within a similar range for a general museum collection.[4]
Moisture has strong effects on nearly all museum object materials, with ceramics and glass being exceptions to these effects in most cases. Metals face the risk of corrosion as RH increases, a risk which is enhanced by surface contaminants and emphasizes the need for proper housing.[3] Additionally, mold growth is far more likely as humidity increases, which not only could cause allergic reactions for viewers but it also weakens the objects afflicted and attracts other pests.[5] In contrast to this requisite for dry conditions, if the atmosphere is not humid enough wooden objects could crack or warp, and many organic materials face embrittlement below 40% RH.[3]
Although minor and gentle fluctuations in RH can reasonably be withstood by most objects, quick or drastic shifts can be harmful. Anistropic materials such as wood and ivory are especially responsive to humidity changes, and RH issues are compounded when they are attached to inorganic materials such as a metal. The metal acts as a restraint, hindering the organic materials’ ability to expand and contract as needed. Thus, objects composed of highly responsive materials or a combination of organic and inorganic materials should ideally be in carefully controlled climates and buffered against the atmosphere by their display or storage housing.[4]
Visual light cannot be eliminated, as it is required both to view objects in detail and to move safely in the presence of objects. Unfortunately, this means that harmful oxidation effects which visual light makes possible also cannot be eliminated, but merely reduced to the amount necessary for the task at hand.[3]
The effects of visual light began to be studied by artists and color manufacturers as early as the 18th century, but it was not until the mid-20th century that the chemical damage caused by different lighting situations was researched in depth. In recent decades the cumulative nature of light degradation has become better understood by conservation science. Comprehensive studies began to emphasize long term effects and allow for short term variation in light levels depending on the specific situation: standard viewing, viewing by the aged, complex study or treatment, and observation of low contrast details all may have different requirements. Practical compromise between protection of cultural artifacts and allowing the artifacts to fulfill their visual purpose means there is an allowance of some physical risk.[6]
Even with this flexibility, light interaction should be limited to moments when an object is on view or undergoing study, and the level of lighting should be chosen accordingly. Because lighting effects are cumulative, any limit in exposure – whether in time or in intensity – prevents material degradation. A period of intense or lengthy light exposure should be balanced out with periods of low exposure.[7]
UV is a form of electromagnetic radiation with higher energy than visible light. Its does not contribute to the accurate viewing of objects and is ideally completely eliminated; otherwise materials may be weakened in any number of ways ranging from yellowing to disintegration. Organic materials, especially textiles and paper, are particularly vulnerable to UV-caused decay.[7] Direct sunlight holds the most potential for UV damage, but certain types of artificial light bulbs may also produce these harmful rays.
Various types of filters have been developed to combat UV interaction with artifacts on display, and many of them can be used in conjunction with each other to reach the optimal setting for a particular collection. Among the first employed were heavy drapes; a simple solution to apply only if an institution can provide employees to open and close the drapes at the appropriate times based on viewer access.[8] Many filtration devices rely on materials that absorb the UV, such as acrylic films or painted wash walls, but in doing this the materials themselves decay and the filters must be replaced. A better solution is interference filters, which can be customized for the setting of intended use to reflect light at such an angle that it cancels out harmful incoming wavelengths. If an interference filter is selected as the appropriate form of filtration, UV is eliminated completely and efficiently.[9]
Every time an object is handled, it is at risk for damage. High standards for general housing and for packing help eliminate direct handling and decrease chances of damage due to contact.
Other than smart structural design, one of the major components of display and storage housing is proper selection of materials. Especially for long-term solutions, the materials that surround an object must not interfere negatively with the materials that compose the object. Experimentation using Oddy tests is a qualitative way to determine whether specific materials undergo deleterious chemical reactions in the presence of one another.[10]
Environmental conditions as explained above are also crucial to housing decisions.
Proper packing techniques and materials are the best way to achieve object safety during transit, and - as with nearly every aspect of preventive conservation - these must be determined in response to the particular objects involved. An ideal shipping container not only provides a shell of protection from shock, vibration, and mishandling, it also helps insulate the interior climate from fluctuating atmospheric conditions and defend against pests. Packing mounts, protective wrapping and cushioning, packing materials, crate size and layers, and means of transport are all variables which a conservator must work into an effective strategy for safe shipment.[11]
Successful moves of the past suggest that the shipment of objects begin with a complete inventory and condition survey of the objects prior to their movement. If a large number of objects are to undergo the transition, it is recommended that a smaller, representative group be sent first to reveal any improvements that can be made for the bulk of objects. All objects should be assessed to determine whether they need stabilization before shipment; it is possible that some should not travel at all due to their condition.[12] Often journeys require several means of transport and transitions from one shipping company to another; therefore, investigation must be done to determine the least reliable portion of the trip, and packing details should revolve around that.[11]
Many collection departments contribute to successful object movements. Conservators, registrars, photographers, and curators should all be involved and help contribute to clear planning and communication throughout the process.[12] Multiple institutions are usually involved as well. The destination of the shipment must be evaluated so that the objects can be prepared adequately for transitions, including considerations for acclimatization and unpacking.[13]
Pests pose a serious threat to cultural artifacts. Whether they feed off of the composition materials or seek shelter within an object, they can cause damage through actively dismantling or consuming the object, staining or dirtying it, weakening structures, or simply by attracting other harmful creatures. Insects, microorganisms, and rodents are the most commonly encountered pests, but in certain locations birds, bats, lizards, and mollusks must be considered a threat as well.[5]
The approach to preventing pest infestation has changed quite a bit in the methodology employed. Where formerly fumigants and pesticides were applied directly to every object, now more passive and less toxic means of pest management are favored. These newer techniques can be just as effective with careful and thorough planning. Different object materials are sensitive to different infestations, so a thorough material understanding of the artifacts to be protected and the pests resident to the area is required. Risks involving the collection building, constructive and decorative materials, and staff activities should be assessed, and a program should then be put in place which reduces these risks.[5]
The simplest way to prevent pests from entering areas of concern is to keep the space uncluttered and sanitary. Additionally, holes or cracks in the building construction should be filled if possible, and deteriorating areas should be repaired or monitored carefully for breaches. All objects brought into the collection should be isolated for a time until it can be confirmed that no pests have traveled with the object. Regular inspections for signs of infestation should take place, and these should be well-documented to track any changes in problem areas and the effectiveness of the system in place.[5]
If an infestation does occur, the response must consider the safety of the cultural material involved. Individual objects can be quarantined through bagging to either contain or prevent infestation. Effective treatments include fumigation, freezing, or pesticides; cost may be the major deciding factor, based on the infestation and the institution.[5]
Every type of disaster - from fires to floods to earthquakes to civil disorder - falls into the category of emergency when it comes to cultural artifacts. These cannot be controlled, of course; however, they can be predicted to a certain extent based on the location of the collecting institution, and the readiness of the institution for extreme situations can be controlled. Many times if a catastrophe strikes, objects cannot be returned to their previous condition, and large numbers of objects face this risk at once. Well-designed display mounts and storage housing, regulated storage space, and rehearsed drill procedures all contribute to effectively mitigating the risks associated with emergencies. Because of the interdisciplinary support such endeavors require, an additional benefit is that separate departments gain a better understanding of each other's roles and how they overlap.[14]
The reformatting or duplication of a cultural object often takes place in the form of photographic documentation. Documentation should take place when an object enters a collection, when it is moved or shipped, and throughout any conservation treatment. In this way it provides a visual reference for future professionals, revealing the original condition and any successive states of the condition. The success or failure of treatments and housing can then be determined and valuable lessons can be applied to future decisions. Most importantly, if anything should happen to the object, whether through disaster or natural decay, a record of its presence and purpose will still remain.[15]